The invention relates to an electric drive, in particular for a pivoting arm, such as a robotic arm, comprising a rotor, a plurality of magnetic periods, and a device for determining the rotational position of the rotor based on at least one measurement signal, which is indicative of the inductance of a pole winding strand that is dependent on the position of the pole winding strand relative to the magnetic periods.
Such an electric drive is known from DE 100 31 423 A1 and DE 046 638 A1. The rotational position of the rotor of an electric motor is determined based on a voltage signal that is dependent on the phase strand inductance. When the electric motor is operated by way of pulse width modulation, such signals can be captured, for example, at the star point of the phase strands, which are connected in a star configuration. Because the phase strand inductance changes periodically in accordance with the magnetic periods, the rotational position of the rotor can thus only be determined within the respective rotational angle range of a magnetic period. In addition, rotational positions can only be determined indirectly by counting the magnetic periods that have been covered. The counted information must not be lost.